I. Technical Field
The present invention relates to a horizontal centrifugal separator including a rotary bowl and a screw conveyor inserted into the rotary bowl. In particular, the invention relates to a horizontal centrifugal separator including sealing means that, while having a simple structure, can improve the hermeticity of a casing containing the rotary bowl and the screw conveyor.
II. Description of the Related Art
A horizontal centrifugal separator referred to as a decanter is one type of known solid-liquid separator that uses centrifugal force. For example, as shown in FIG. 1, a decanter 1 has a basic structure in which a rotary bowl 11 rotatable about its horizontal axis and a screw conveyor 12 inserted into the rotary bowl 11 are contained in a casing 2 serving as an exterior casing. The casing 2 is separated into a lower casing 21 having a solids outlet 21a and a separated-liquids outlet 21b formed in the lower part thereof and an upper casing 22 detachable from the lower casing 21. The lower casing 21 and the upper casing 22 have flanges 23 formed along the respective opening edges thereof. The casing 2 having a substantially cylindrical shape is formed by securing the flanges 23 to each other with securing means 24 such as bolts.
Openings 25 having, for example, a circular shape are formed in the opposite end faces of the casing 2, and the rotary shafts of the rotary bowl 11 and the screw conveyor 12 extend through the openings 25 and are rotatably supported by bearing means 13. Mechanical seal housings 14 for sealing the rotary shafts are disposed in the openings 25, and O-rings 15 provided on the outer circumferences of the mechanical seal housings 14 hermetically seal the gaps between the mechanical seal housings 14 and the openings 25.
The barrel portion of the rotary bowl 11 is composed of three portions, i.e., a cylindrical portion on a first end side thereof, an intermediate conical portion, and a circular portion on a second end side. The portion formed into a conical shape forms a beach portion in which solids conveyed by the screw conveyor 12 are separated from liquids and are thereby dewatered. The cylindrical portion on the first end side forms a screen portion for washing the dewatered solids with washing water, and the washed solids are discharged through solids outlets 16. The cylindrical portion on the second end side forms a pool (fluid pool) portion for reserving a feed fluid supplied to the inside of the rotary bowl 11 and has separated-liquids outlets 17 formed in the end face thereof. A screw vane 18 and feed fluid supply ports 19 are formed in the barrel portion of the screw conveyor 12 inserted into the rotary bowl 11, the feed fluid supply port 19 being provided for supplying the feed fluid fed from a feed fluid supply nozzle 3 to the rotary bowl 11 through the action of centrifugal force.
In the structure described above, by transmitting the power of a motor 32 serving as a driving mechanism to a pulley 33 through a rotary belt 31, the rotary bowl 11 is rotated at a predetermined rotation speed. When the feed fluid is supplied to the pool portion while the rotary bowl 11 is rotated, the solids are settled out through the action of the centrifugal force. The solids are conveyed to the beach portion by the screw conveyor 12 rotated through a gearbox 34 used as a differential speed generating mechanism and are then dewatered. The dewatered solids are then washed with washing water from washing water injection ports 35 when they pass through the screen portion. The washing drainage used for washing the solids is discharged through discharge holes 36 formed in the screen portion. The solids having been washed in the screen portion are discharged from the solids outlets 16 and are then discharged to the outside of the separator through the solids outlet 21a. The liquids separated from the solids (separated liquids) are discharged from the separated-liquids discharge outlets 17 and are then discharged to the outside of the separator through the separated liquids outlet 21b. FIG. 1 shows the decanter of the screen bowl type. However, decanters of the solid bowl type that do not have the screen portion are also widely known.
As described in, for example, patent documents such as Japanese Patent Application Laid-Open No. 2007-44671, a number of studies have previously been conducted to improve the sealing properties of mechanical seals. However, only a few studies have been made to ensure the hermeticity between the mechanical seal housing 14 and the casing 2, which are non-rotating mechanisms. If the set pressure is increased, leakage can occur between the mechanical seal housing 14 and the casing 2. Therefore, in horizontal decanters having a casing structure composed of two separated (upper and lower) casings, the internal pressure thereof during use is limited to several tens kPa or less. At present, when the internal pressure reaches a higher level, the treatment is performed using decanters having an integral cylindrical structure or vertical decanters. However, in decanters having an integral cylindrical structure, the rotary members must be pulled out in the axial direction thereof when disassembled. Therefore, such decanters have drawbacks in that the assembling-disassembling process is complicated and that a sufficiently large space must be provided for maintenance. In particular, decanters of the screen bowl type in which the ratio between the diameter and length of the bowl is large have an influence on the size of buildings. Accordingly, the integral cylindrical structure has not practically been used in such decanters.